Direct reaction description of sub- and above-barrier fusion of heavy ions

A new approach to calculation of the fusion cross section σF, based on the direct reaction concept, is presented. The method is to define a fusion potential WF [with r{≤}RF=rF(A₁1/3+A₂1/ 3)] as a part of the imaginary potential of the usual optical model. The σF is then obtained as that part, due to only WF, of the total absorption cross section. It is seen that, if rF is chosen as 1.40--1.50 fm, the value of σF computed as described fits the experimental σF very well, in both sub- and above-barrier regions, and for a variety of fusing nuclear pairs A₁ and A₂. In most cases, it is sufficient to consider only the incident (elastic scattering) channel. In a few cases, in which some specific nuclear structure effects are involved, it is found necessary to perform coupled-channel calculations. Then absorption due to other channels is also taken into account explicitly. It is shown that adding these contributions is the key to getting good fits to data, under the above-mentioned special circumstances. A possible relation of what the present approach describes, particularly when it is used in the sub-barrier region, to (spontaneous) fission is also discussed.